How to take flats?

[PhoenixRising]

OK,

So I've got a t shirt elastic banded to my scope, pointing to a clear bit of sky waiting for dusk to arrive. Whats the best ISO setting to use, is it 100?

Also, I've always taken my astropics (all 3 of em!) with AWB set to auto, some people have said Tungsten or Daylight are better options, what do you think?

Finally, am I right in thinking that I'm slightly overexposing these flat shots to get the histogram into the middle?

Ta, lets hope it clears tonight...

[Dave Smith]

I usually do my flats AFTER taking the lights etc. Should it not be clear for a few nights (quite possible) you would likely need to remove the camera in which case you would need to do them again. I also do mine in full daylight and set my camera, a DSLR, to do automatic exposure. It has been left on the same iso as for the lights but what you suggest may well be better?

As my camera has been modded I leave it on custom WB but as the files are in RAW, I'm not sure that it matters.

I am no expert at this, but that is the procedure I follow and it seems to work.

Dave

[swag72]

Flats should be taken at the same time as your images that you are using them for. Then you will have the same focus, camera orientation etc. This will ensure that they best match the lights that you are using them with. To that end, you use the same ISO and WB as you use in the image.

[PhoenixRising]

OK. So more work to do in the cold! I just asked because I've googled it and some people do them at dusk. So, I use a Canon 500D. Is it best to leave it on AWB for Colour balance?

[Dave Smith]

If you take RAW files the colour balance does not matter. RAW files are much prefered to jpegs.

Dave

[PhoenixRising]

Thats ok then, I do use RAW files. So I'll do them just after the session, with my laptop screen held up to the tube at the same iso, in AV mode and take about 20. Then take my darks, again, about 20. Does that sound about right?

[Dave Smith]

Sounds good to me.

Dave

[PhoenixRising]

Cool. I'll give it all a go the next time we have a clear night......

Thanks Dave and Swag